In the use of mining and tunnelling machines equipped with cutters or bits in underground mining sparking occurs, particularly when working in harder formations, where the cutter contacts the formation. Under unfavorable conditions, these sparks can lead to the ignition of explosive gas mixtures. Such sparking in the working area is exceedingly undesirable, particularly in coal mining. Efforts are, therefore, made to eliminate the sparking in the working area of the cutter as far as possible by supplying a coolant such as water.
Attempts have already been made to eliminate the sparking in the working area of the cutters by spraying the cutting head with water. Since the engagement area of the cutters on the formation to be extracted is not cooled directly, this method has not yet proved particularly successful.
It has further been proposed to spray water or another coolant behind each individual cutter tip and thus to directly cool the cutter working area. Admittedly, this suppresses sparking very effectively but results in a large accumulation of coolant which is extremely undesirable in underground working.
To reduce the high water accumulation in the case of individual spraying of the cutters, it has already also been proposed to provide the coolant passages to the spray nozzles with shut-off means which are in controllable dependence upon the application of a pressure load to the cutter in such a manner that the coolant spraying of the cutter working areas takes place only during the actual working engagement with the formation, whereas during the cutter idling the coolant spraying is cut off. However, this holder has a relatively complicated and expensive structure with which, for example, on disturbance of the coolant supply, it is very difficult or impossible to replace individual parts.
The problem underlying the invention is to provide a cutter holder of the type mentioned at the beginning whose spraying means, which switches off when the cutter is idling, is reliable and the parts of which mainly prone to trouble and wear can easily be replaced without having to replace the entire holder.